1. Field of the Invention
This invention relates generally to a method and apparatus for conditioning a clock signal, and, more particularly, to a method and apparatus for filtering a clock signal to reduce both broad and narrowband noise.
2. Description of the Related Art
Over time, electronic devices have evolved from relatively simple units to more complex devices. A typical modern electronic device is constructed of numerous subassemblies, each performing its own separate task, but collectively interoperating to control the overall operation of the device. For example, a modem electronic device may include a processor subassembly and a memory subassembly. During the operation of the electronic device, the subassemblies must be able to communicate with one another to exchange information or data. To achieve this communication or interoperation, the functioning of the various subassemblies must be carefully coordinated. For example, the processor subassembly must know precisely when the memory subassembly is providing requested information. Typically, this coordination of the subassemblies is accomplished by synchronizing the operation of the subassemblies through a reference or clock signal.
Typically, a clock signal oscillates at a preselected frequency and the subassemblies are constructed to time their various operations relative to a transition in the clock signal. That is, the operation of each subassembly is configured to perform its functions in synchronism with a common transition or clock edge of the clock signal. Accordingly, proper operation of modern electronic devices is critically dependent upon highly accurate clock signals. Even minor variations in the timing of these clock edges can reduce the performance of the device or even cause its operation to fail. Electronic disturbances, such as noise, on the clock signal can cause mistimed or faulty operation of the subassemblies, or at least problems with interoperability.
Thus, analog clock signals are commonly filtered to remove spurious transitions caused by noise. Filtering, however, can reduce the precision of a clock signal; particularly where the clock signal is a digital square wave, such as is stylistically represented by the waveform of FIG. 1A. For example, applying a relatively narrow bandpass or notch filter to a square wave clock signal distorts the square wave clock signal by rounding off edges and extending the time period for the transition, as shown in FIG. 1B. This distortion can affect the timing of the clock edges, and thus, interoperability of the subassemblies may be compromised.
The present invention is directed to overcoming, or at least reducing, one or more of the problems set forth above.